Proc. Natl. Acad. Sci. USAVol. 90, pp. 2291-2294, March 1993Medical Sciences

Pathology of inhalational anthrax in 42 cases from the Sverdlovskoutbreak of 1979

(Bacillus anthracis/hemorrhagic mediastinitis/hemorrhagic thoracic lymphadenitis/epidemic/Russia)

FAINA A. ABRAMOVA*, LEV M. GRINBERGt, OLGA V. YAMPOLSKAYAt, AND DAVID H. WALKER§1

*Department of Pathology, Hospital 40, Ekaterinburg, Russia; tDepartment of Pathoanatomy, Tuberculosis and Pulmonary Diseases Unit, Ekaterinburg,Russia; tDepartment of Infectious Diseases, Central Postgraduate Institute, Botkin Hospital, Moscow, Russia; and §Department of Pathology, University ofTexas Medical Branch, Galveston, TX 77555-0609

Communicated by Matthew Meselson, December 14, 1992

ABSTRACT A large epidemic of anthrax that occurred inSverdlovsk (now Ekaterinburg), Russia, in 1979 resulted in thedeaths of many persons. A series of 42 necropsies, representinga majority of the fatalities from this outbreak, consistentlyrevealed pathologic lesions diagnostic of inhalational anthrax,namely hemorrhagic necrosis of the thoracic lymph nodes in thelymphatic drainage of the lungs and hemorrhagic mediastinitis.Bacillus anthracis was recovered in bacterial cultures of20 cases,and organisms were detected microscopically in the infectedtissues ofnearly all ofthe cases. A novel observation was primaryfocal hemorrhagic necrotizing pneumonia at the apparent portalof entry in 11 cases. Mesenteric lymphadenitis occurred in only9 cases. This remarkably large series demonstrated the fullrange of effects of anthrax bacteremia and toxemia (edemaespecially adjacent to sites of extensive infection and pleuraleffusions) and hematogenously disseminated infection [hemor-rhagic meningitis (21 cases) and multiple gastrointestinal sub-mucosal hemorrhagic lesions (39 cases)].

Beginning early in April 1979, there was a sudden outbreakof an unknown disease among the population of Sverdlovskin the former Union of Soviet Socialist Republics. In thislarge industrial city just east of the Ural Mountains, themajority of the patients resided in a limited area on thesouthern edge of the municipality. International interest wasdrawn by the suspicion that the epidemic might have resultedfrom release ofa biologic agent from a military facility locatedin the district where the majority of the patients lived. Apublication in May 1980 attributed the epidemic to cutaneousand gastrointestinal exposure to meat from animals infectedwith Bacillus anthracis (1).

Little further information has been published. In fact, thehospital records of the patients affected by this outbreakincluding the autopsy reports were removed from the hospital.Notes describing the details of the gross observations in theorgans at the autopsies of 42 persons in this epidemic werekept in the personal possession of two of the participatingpathologists (F.A.A. and L.M.G.). The microscopic slides,paraffin blocks, and tissue samples from the necropsies werealso kept in a secure location. A substantial collection ofrepresentative examples of the diseased organs was alsomaintained for demonstration. A series of detailed articles onthe macroscopic lesions, microscopic lesions, and causes ofdeath will be published in the Russian medical literature (2).This preliminary report has the purpose of providing in theEnglish language the major observations in a timely manner.

MATERIALS AND METHODSDuring the period of 1 week in June 1992, the four authorsreexamined together the glass microscopic slides and the

available gross organs and evaluated the correlations withnotes made in 1979 ofthe gross descriptions of each necropsyand the microscopic observations for that case. Cultures hadbeen taken for identification of bacterial agents. Bacteriawere searched for microscopically in sections stained withhematoxylin and eosin in all cases. Sections cut from sixblocks were stained by the Brown-Brenn and Brown-Hoppsmethods for demonstration of Gram-positive and Gram-negative bacteria (3, 4).

RESULTSThe initial diagnosis of anthrax was made by the pathologist(F.A.A.) in case 1 of this series on the basis of the remarkablyhemorrhagic meningitis in a patient who died on approxi-mately the sixth day of the epidemic. The diagnosis wasconfirmed by demonstration of bacilli on smears prepared atnecropsy on the same day (April 10, 1979) and definitivelydocumented by identification of B. anthracis in cultures onApril 11.

This series of 42 autopsies represents a striking illnessaffecting previously healthy persons, who died usually aftera rapid course of 1-4 days duration (Table 1). All 42 caseswere characterized by the most prominent and consistentlesions ofhemorrhagic thoracic lymphadenitis (Figs. 1-3) andhemorrhagic mediastinitis (Figs. 3 and 4). Spread of B.anthracis to the peribronchial lymph nodes by the lymphaticvessels was emphasized by the presence of the organisms inthe marginal sinus where the afferent lymph first enters thelymph node (Fig. 5). The pulmonary portal of entry wasfurther emphasized by the presence of a primary anthraxpulmonary focus-i.e., focal hemorrhagic, necrotizing an-thrax pneumonia in 11 patients.There were various manifestations of hematogenous

spread of B. anthracis infection including serohemorrhagicand hemorrhagic leptomeningitis (21 cases) (Figs. 6 and 7).Gastrointestinal lesions were observed in 39 cases, most ofwhich appeared to represent multifocal hematogenous spreadofB. anthracis to the submucosa of the gastrointestinal tract,in particular to the small intestine, stomach, and colon (Figs.8 and 9). The lesions did not involve the Peyer's patches.Mesenteric lymph nodes demonstrated hemorrhagic involve-ment in only 9 cases.A remarkable effect of the disease was edema and other

evidence of increased vascular permeability including gelat-inous edema of the mediastinum, pleural effusions, lepto-meningeal edema, and pulmonary edema. B. anthracis was

observed in the lesions of serohemorrhagic nature, andanthrax toxins secreted by these organisms were consideredto be the cause of the vascular damage resulting in hemor-rhage and serious exudate.

ITo whom reprint requests should be addressed.

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Table 1. Forty-two patients with inhalational anthrax inSverdlovsk in 1979

B.anthracisidentifi-

Date cation Pathology

Age/ Admis- Cul-sex

42/M67/M68/F38/M47/M68/M25/F66/F50/M65/M48/M42/M40/M52/M37/M32/M52/M68/F71/F58/F42/F49/M43/M68/F44/M39/M46/M50/F45/M39/M42/M42/M48/M33/M32/M55/M33/M43/M25/M30/M29/M¶/M

Onset

4/74/74/8

4/94/104/104/124/104/11

4/124/104/13

4/15

14/144/144/154/154/15

4/17

4/204/214/214/224/25

4/274/295/45/75/95/12

sion

4/104/84/94/8

4/124/134/134/134/134/13

4/134/134/144/16

4/134/164/154/22

4/21

4/234/24

4/285/14/305/65/12

5/15

Death ture

4/10 +4/9 §4/10 +4/8 §4/12 +4/13 -

4/13 +4/13 +4/13 -

4/14 -

4/14 -

4/14 +4/14 +4/14 +4/15 -

4/15 -

4/16 -

4/16 -

4/15 -

4/25 -

4/17 -

4/16 +4/16 -

4/30 -

4/18 +4/19 +4/21 +4/25 -

4/22 -

4/23 +4/24 -

4/24 +4/24 +5/3 -

4/28 +5/1 -

4/30 +5/10 -

5/12 +5/10 +5/16 -

11 +

Hist- HEM HEMology LN* MEDt+ + +¶ + ++ + +§ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + +¶ ,+ ++ + +_ + +

+ + ++ + ++ + +_ + +

+ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + ++ + +¶ + ++ + ++ + ++ + +¶ + ++ + ++ + ++ + ++ + +

MEN*

+

+

+

+

+

+

+

§

*Hemorrhagic thoracic lymphadenitis.tHemorrhagic mediastinitis.tSerohemorrhagic and hemorrhagic meningitis.§Not examined.$Unknown.IFound dead and autopsied on 6/15, with preservation of tissues andcondition of the body suggesting a short interval between death andnecropsy.

DISCUSSION

The pattern of lesions in these 42 cases of fatal anthraxbacteremia and toxemia from Sverdlovsk is typical of inha-lational anthrax in experimentally infected nonhuman pri-mates (5) and in epidemiologically diagnosed humans (6-13).The pathogenesis ofB. anthracis infection that enters via thenormal lung begins with transport of spores to the peribron-chial and mediastinal lymph nodes (8, 14). After germinationof the spores, the bacteria replicate and secrete the three

FIG. 1. The cut surface of the lungs, trachea, and hilar lymphnodes in case 41 reveals massive hemorrhagic enlargement of theperibronchial and carinal lymph nodes with extension of the hem-orrhage into the adjacent tissues including the submucosa of thebronchi and trachea.

components of the toxin: protective antigen, edema factor,and lethal factor (15-17). Thus, inhalational anthrax is char-acterized by the severe local effects of the toxin at its primarysite of production, thoracic hemorrhagic necrotizing lym-phadenitis and hemorrhagic necrotizing mediastinitis, as wellas the systemic effects of bacteremia and toxemia. Thesethoracic lesions are not expected to occur in toxemic cuta-neous or intestinal anthrax because spread from the cutane-ous or intestinal portal of entry by the lymphatic vesselswould involve the regional lymphatic drainage of the primaryskin or intestinal lesion, but there would be no spread to thelymphatic drainage of the lungs in the mediastinum. In 11cases of the present series, there was a single primarypulmonary lesion analogous to the Ghon focus in the moreslowly developing infection, tuberculosis.The gastrointestinal lesions appear to be mainly, or pos-

sibly wholly, hematogenous in origin. The lesions are cen-

FIG. 2. Photomicrograph of a peribronchial lymph node of case39 reveals marked dilation of the marginal and draining sinusesbecause of the presence of protein-rich edema and hemorrhage.(Hematoxylin-eosin stain; x90.)

No.

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Proc. Natl. Acad Sci. USA 90 (1993)

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Proc. Natl. Acad. Sci. USA 90 (1993)* , : , ''.-.i . : .>. _ _ > ' > :S^ ......................... ..FIG. 3. Photomicrograph of a thoracic lymph node with hemor-

rhage and necrosis and adjacent hemorrhagic mediastinitis in case 39.(Hematoxyhineosin stain, x25.) (Inset) Higher magnification pho-tomicrograph of the same section demonstrates lymph node necrosiswith karyorrhectic debnis, macrophages containing anthracotic pig-ment, and B. anthracis organisms. (Brown-Brenn stain; X375.)

tered in the submucosa where the blood supply is mostprominent. These lesions are analogous to the submucosalmetastases of hematogenously disseminated highly malig-nant neoplasms. The mucosa was present over even thelargest hemorrhagic lesions that in some cases extendedthrough the muscularis propria, further suggesting that theinfection amrved in the submucosa via the bloodstream ratherthan entering the mucosa from the gastrointestinal lumen. Infact, Gram-positive bacilli were observed microscopically inblood vessels of the intestinal submucosa. In 4 of the 11reported cases of the pathology of fatal inhalational anthraxpublished in the English language since 1960, intestinallesions presumably of hematogenous origin were described(6, 7, 9, 10-13). Moreover, the classic Russian pathology textby Davidovsky (18) emphasizes that in 90% of cases withgastrointestinal lesions, the enteric pathology occurs becauseof hematogenous spread of bacilli from a cutaneous orrespiratory portal of entry. Although a study of the pathologyof epidemiologically diagnosed intestinal anthrax is lacking,the best data available suggest that the primary lesion ofintestinal anthrax is usually solitary and located in theterminal ileum or cecum (19). The lesions in the present seriesof cases usually were numerous and involved many regionsof the gastrointestinal tract, including in most cases thestomach and jejunum, indicating that the gastrointestinal

MM,"A~~~~~~~~~~4

T~FIG3 Phtmcorp of a thoaci lymp. no*dXewth emr

with~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.kayrhcideri, marohae cotiig ath,racotic...men, an . anthaci oraim. (Bron-Ben stain I35

tere in th sumcs wherelth b,.loo..,dsuppl'-is'!most' '

prmnet Thes''"e,s"...,", nsare anloou to th submcosametastases of heaoenul disseminated hihymlgnantneplsm. Th muos wa preen over.even thelagst heorhai leson tha in som case exene

FIG. 4. Photomicrograph of a cluster of Gram-positive B. an-thracis in a hemorrhagic area of the mediastinum of case 39.(Brown-Brenn stain; x375.)

. 4,W4' d

FIG. 5. Photomicrograph of the marginal sinus of a thoraciclymph node in case 39 that is distended by lymph and contains manyB. anthracis organisms, some of which appear Gram-positive (dark)while others appear Gram-negative (lighter bacilli and filaments).(Brown-Hopps stain; x250.)

involvement was most likely hematogenous. In 9 of ourcases, the route of spread from the pulmonary portal of entryincluded lymphogenous spread to the mediastinal lymphnodes, followed by hematogenous spread to the intestinalwall and subsequent lymphatic spread to the mesentericlymph nodes, which were less severely involved than thethoracic lymph nodes. Unfortunately, there is a paucity ofinformation regarding the pathology and pathogenesis ofprimary intestinal anthrax for comparison with our cases(18-26).The tragedy of these deaths is compounded by the condi-

tions of secrecy that have impeded elucidation of many factsthat potentially would be useful in the future diagnosis andtreatment of inhalational anthrax. The paucity of clinicalinformation impairs extensive clinicopathologic correlationsincluding the effects of various therapeutic approaches.Some deaths occurred outside the hospital, at home, or evenin the street or in a field. Medical personnel accompanyingthe emergency transport vehicles often made an initial diag-

FIG. 6. Photomicrograph of the brain from case 41 shows mark-edly hemorrhagic leptomeninges. (Hematoxylin-eosin stain; xlS.)

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>O..g ~ ~ M~ .,*,* . g < .. r .

4~~~~~ V.i.',,'a fvSs ':"Sni,

114

FIG. 7. Photomicrograph of the leptomeninges of case 41 revealsmany B. anthracis organisms and marked hemorrhage. (Brown-Hopps stain; x210.)

nosis of pneumonia. The chest pain, which was severeenough to suggest an initial diagnosis of myocardial infarc-tion, undoubtedly resulted from the hemorrhagic thoraciclymphadenitis and mediastinitis.

Previous reports ofthe cases in this outbreak have excludeddescription of the thoracic pathology (1). The availability ofthese new data leads to the conclusion that these patients diedbecause of inhalation of aerosols containing B. anthracis.Description of cases of cutaneous anthrax suggests that some,if not all, might have been acquired from animals infected bythe same source of spore-containing aerosol. None of thesecases of cutaneous anthrax, which is usually not fatal, wererepresented in this large autopsy series.

We thank Ms. Wendy DuPriest for secretarial assistance in thepreparation of the manuscript. This investigation was supported inpart by a grant from the John D. and Catherine T. MacArthurFoundation to Matthew Meselson for a continuing study of theSverdlovsk anthrax epidemic of 1979.

FIG. 8. (Left) Photomicrograph of a substantial focus of submu.

cosal hemorrhage in the small intestine that extends into the mus-

cularis propria in case 6. The overlying mucosa is still visible.

(Hematoxylin-eosin stain; x 13.) (Right) The area of submucosal

intestinal hemorrhage contains B. anthracis organisms. (Brown-

Hopps stain; x250.)

FIG. 9. Photomicrograph of the submucosa of the small intestineof case 6 shows small blood vessels that contain B. anthracisorganisms. (Brown-Hopps stain; x 300.)

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